Yeah, Empires are a good idea. HRE and Byzantium should of course have their own mechanics, but I want the ability to create ahistorical empires as well with a really succesful king.
Yes after all one way of looking at the creation of the HRE was that it was created when someone combined the titles of King of France, Burgundy and Germany.
In a simillar way when your King gets too big for his boots there should be some way to celebrate it.